Respiratory illness encompasses a broad range of ailments, including viral infections such as cold and flu, as well as allergies, sinusitis, rhinitis, and the like. Respiratory illness may present as any of a variety of symptoms, such as runny nose, nasal or chest congestion, cough, sneezing, pressure, headache, aches, fever or sore throat. Pharmaceutical actives typically used to treat these symptoms generally fall into one of the following pharmaceutical classifications: antihistamines, decongestants, antitussives, expectorants, demulcents, anesthetics, analgesics, antipyretic and anti-inflammatory agents. The products for treating respiratory symptoms associated with respiratory illness are manufactured in a number of product forms, the most common being liquid syrups and elixirs for swallowing, mouth and throat drops and lozenges, tablets, caplets, capsules, and liquid-filled capsules and lozenges, effervescent tablets, and dry dissolvable powders, as well as inhalants and topical creams and lotions that release volatile agents that are inhaled through the nose into the respiratory tract. The oral compositions are typically swallowed immediately, or slowly dissolved in the mouth.
Products for relief of multiple symptoms may include various pharmaceutical actives such as pseudoephedrine, phenylephrine, and phenylpropanolamine (decongestants), guaifenesin (an expectorant), chlorpheniramine, diphenhydramine and doxylamine (antihistamines), dextromethorphan (cough suppressant), acetaminophen, ibuprofen, and aspirin (analgesics). Because these actives have different properties and stabilities, it is a challenge to formulate overall compositions containing actives wherein the actives are all stable and effective. In particular, the stability of certain pharmaceutical actives has been an on-going problem, especially when formulated in combination with other actives. Often, for example, liquid solutions discolor or one or more actives precipitates out of solution or is degraded. To illustrate, wherein phenylephrine is desired as a pharmaceutical active, one of the common problems associated with the formulation and use of phenylephrine is degradation. Phenylephrine may degrade in the presence of oxygen, aldehydes, certain acids including citric acid, and metals. The degradation of phenylephrine, even in solid dose forms, has also been reported.
Thus, there is an ongoing need for stable, effective compositions useful for the treatment of respiratory illness and associated symptoms.